WO 9635906 A1 describes a coupling for hydraulic ducts with a female coupling and a male coupling. The female coupling has a receptacle, into which the male coupling can be inserted through an opening in the receptacle. An inner circumferential groove is provided in the opening. A multitude of locking elements is inserted into the opening. The locking elements, in form of annular segments, are distributedly arranged around the circumference of the inner circumferential groove. The locking elements are supported in the circumferential direction on each other. Thus, the locking elements are held in the inner circumferential groove. The locking elements are springingly acted upon towards the inside by means of an elastic O-ring at the end of the inner circumferential groove, distanced from the opening. The locking elements form, in a locking position, a conical inner circumferential face and project partially from the inner circumferential groove to the inside.
The male coupling has a displacement face on its end. The displacement face interacts with the inner face of the locking element so that they are pivoted from the locking position towards the outside into a releasing position. In this position, the locking elements are completely arranged within the inner circumferential groove. Thus, the male coupling can be inserted into the opening. The male coupling, further, has an outer circumferential groove. The locking elements are pressed into the outer circumferential groove by means of the elastic O-ring, as soon as the male coupling is inserted far enough into the receptacle. In this position of the male coupling, the locking elements are axially supported on one side by the support face of the inner circumferential groove and on the other side by a locking face of the outer circumferential groove. Thus, the male coupling is retained against withdrawal.
A plastic ring is provided within the outer circumferential groove of the male coupling. The ring is narrower than the outer circumferential groove. If the male coupling is inserted further into the receptacle, the locking elements slide on the outer circumferential face of the plastic ring. Thus, the locking elements are moved into the releasing position. Since the friction force between the locking elements and the plastic ring is higher than the friction force between the plastic ring and the male coupling, the plastic ring glides, when withdrawing the male coupling, within the outer circumferential groove, until the plastic ring abuts the locking face of the outer circumferential groove. The outer diameter of the plastic ring is at least as large as the outer diameter of the male coupling at its end. Thus, when further pulling out the male coupling, the locking elements glide from the plastic ring onto the outer circumferential face of the male coupling and the male coupling can be completely pulled out.
A disadvantageous of this coupling is that when a locking element is lost, the residual locking elements are not held in the inner circumferential groove since they no longer support each other. Furthermore, the assembly of the individual locking elements is difficult because they must mount so that they support one another. Furthermore, the plastic ring is loaded by a high mechanical force during the coupling procedure. Thus, the outer diameter of the plastic ring may be reduced by wear off. Accordingly, it becomes smaller than the outer diameter of the male coupling. Due to wearing, a jamming of the male coupling may occur during withdrawal.
DE 199 32 307 A1 discloses a coupling with a female coupling having a receptacle to receive a male coupling. A circlip sits in an inner circumferential face of the receptacle. The circlip projects with a portion of its cross-sectional face protecting radially to the inside. The male coupling has, on its end, a displacement face. The displacement face pushes the circlip radially deeper into the inner circumferential groove during the insertion of the male coupling into the receptacle. This enables insertion of the male coupling. The male coupling has an outer circumferential groove. The circlip, after further insertion of the male coupling, enters into the outer circumferential groove. In this position, the circlip is supported axially on one side by the locking face of the outer circumferential groove and on the other side by the locking face of the inner circumferential groove. Thus, the male coupling is retained against withdrawal.
Starting from the receptacle opening, an annular gap is formed between the female coupling and the male coupling. An unlocking sleeve is inserted through the gap into the receptacle. Due to axial displacement of the unlocking sleeve into the receptacle, the circlip is axially moved along the conical locking face of the outer circumferential groove. Thus, the circlip is radially pushed out off the outer circumferential groove so that the male coupling can again be removed from the receptacle.
Since the locking face of the outer circumferential groove is formed as steep as possible towards the longitudinal axis, the angle that the conical locking face encloses is as large as possible. This ensures the best possible axial support of the circlip between the locking face of the outer circumferential groove and the locking face of the inner circumferential groove. A high force is necessary to push the circlip out off the outer circumferential groove. Furthermore, there is a danger that the circlip maybe widened. Thus, the circlip would not widened round, because it would be cut at one position. Thus, the ends of the circlip can lock between the locking faces.